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Investigating the Effect of Temperature on Rate of Respiration in Yeast

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Introduction

Investigating the Effect of Temperature on Rate of Respiration in Yeast Plan ATP. Glucose is the main energy source, and can be broken down in four different stages: Glycolysis, the link reaction, the Krebs cycle, and oxidative phosphorylation. Yeast is an organism that actively respires aerobically. But it can respire anaerobically, when deprived of oxygen. But anaerobic respiration is not as efficient as aerobic respiration, because oxidative phosphorylation requires a constant supply of oxygen for it to occur; also the link reaction and the Krebs cycle need oxygen. Therefore the link reaction, Krebs cycle and oxidative phosphorylation only work in aerobic conditions, whereas glycolysis can work in anaerobic conditions also. Glycolysis means 'sugar-splitting'. In glycolysis, there is a net gain of 2 ATP molecules. You must start with a hexose sugar, such as glucose. The glucose molecule will undergo phosphorylation. Phosphorylation involves ATP molecules being broken down into ADP and their phosphates are attached to the glucose molecule. The first ATP causes the hexose sugar to be turned into hexose phosphate, and the second ATP molecule makes it hexose bisphosphate. Phosphorylation raises the energy of the glucose, and reduces the activation energy barrier for the pathway. After phosphorylation, the hexose bisphosphate is split into 2 other identical molecules of triose phosphate. Hydrogen is removed from the triose phosphate using dehydrogenase enzymes, and the hydrogen is taken by an NAD molecule. NAD is a hydrogen acceptor or a coenzyme molecule, and is reduced when it takes hydrogen. ...read more.

Middle

This was because the kinetic of the particles was increased they started to vibrate vigorously and the enzymes were slowly denatured. So if the yeast was left in the temperature for longer more enzymes would have denatured, causing the rate of respiration to decrease even more. From 35�C - 40�C the rate of respiration is fairly fast, and is the steepest slope in the entire graph. This proves my theory that the optimum temperature for most enzymes is 37�C. From 40�C - 45�C the rate of respiration decreases, but only a slight decrease is noticeable. But in my theory it is written that at this point the enzymes should be denaturing. I still believe my theory to be true, because I believe that the enzymes were not given enough time to denature fully. From 45�C and onwards there is quite a clear decrease in the intensity of the slope of the graph, this is because the temperature is high enough so that the kinetic energy of the particles is large enough for the enzymes to denature quite quickly. I was required to how the temperature affects the rate of respiration in yeast. I can conclude that as the temperature increases, the rate of respiration increases due to the faster motion of the particles. But after the optimum temperature of between 35�C - 40�C is reached, the enzymes will slowly begin to denature and the rate of respiration will decrease from there onwards. ...read more.

Conclusion

This could have caused my anomalous results to come about. Adding methylene blue had to be done carefully so I didn't accidentally add more than 3 drops, this was done accurately by me, so it could not have been a source of error. But the volume of the drops probably always varied from drop to drop. If three small drops were put into a yeast suspension which had more yeast suspension in it by human error, the methylene blue indicator would disappear much faster. This source of error could have been another reason for my anomalous results. Over the two days there was a variety of methylene blue bottles available to me. If I used two different bottles over the two days, the concentrations could be varied, due to contamination or dilution. This would have seriously affected my results, and could have led to my anomalous results. Other small things could have affected the results and could have caused anomalies. The syringe may not be entirely clean for every repetition, because it is used over about 15 times. I could not clean it with water, or else water may contaminate it, causing the yeast suspension to become slightly dilute on some occasions. There was a small amount of methylene blue remaining on top of the solution. This methylene blue was reacting with the oxygen in the air. The temperature in the water bath may not have been entirely uniformly distributed, due to little mixing. Accuracy of resultsc ...read more.

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